This invention relates to an integrated optical switch with moving parts, an optical cross connecting device using the switch, and a process for making the switch.
Optical cross connecting devices can be compared with multiplexers capable of optically selectively connecting one or several optical input channels to one or several output channels. They use optical switches for this purpose.
The invention also relates to on/off type switches, in other words switches that enable or disable the passage of light, and switches that reflect light, or switches that modify a characteristic of light. The switches may have two or more switching states.
Many applications of the invention are in the field of optical telecommunications and optical signal processing.
Documents (1), (2) and (3) for which the complete references are given at the end of the description, give an illustration of a technological background of the invention.
Document (1) describes a multichannel optical switch equipped with a flexible distribution beam. This beam is provided with an optical microguide, and distributes a light beam applied at an input channel to one output channel selected among several possible output channels.
The use of this type of switch to make an optical cross connect necessitates a large number of components, and therefore a large number of electronic control circuits for these components. Furthermore, the switch creates large optical losses.
A smaller number of components may be used in an optical cross connect of the xe2x80x9cin free spacexe2x80x9d type. In this type of cross connect, for example described in document (2), switches with vertical xe2x80x9ctorsionxe2x80x9d mirrors are used.
The vertical mirrors may occupy a first switching position corresponding to a light reflection mode, and a second switching position corresponding to a light transmission mode.
The mirrors are placed perpendicular to a main face of a support substrate. They may pivot about an axis which is also perpendicular, between two switching positions. The mirrors are moved by applying electrostatic forces between a mirror support plate and a vertical electrode.
In this type of switch, control of the verticality of the mirrors may be critical. A verticality fault of a mirror may cause misalignment of the optical beam reflected by the mirror.
Document (3) also describes a switch in which a mirror is pivoted by electromagnetic forces from a rest position parallel to the substrate, towards an active position perpendicular to the substrate. In this case also, there is the problem in keeping the mirror in its active position while guaranteeing that this position can be maintained with precision.
The purpose of this invention is to propose an improved optical switch that does not have the difficulties mentioned above and in which the active position of a mirror or another optical means may be fixed precisely.
Another purpose is to propose a switch that may be an on/off type switch but that can also be designed to have several switching states.
Another purpose is to propose a particularly simply and economic process for making such a switch.
Finally, another purpose of the invention is to propose an optical cross connecting device using the improved optical switch.
More precisely, the objective of the invention to achieve these purposes is an integrated optical switch comprising optical means capable of interacting with a switching light, and driving means connected to the optical means to make them pivot between a first xe2x80x9crestxe2x80x9d position and a second xe2x80x9cactivexe2x80x9d position, all fixed on a substrate. According to the invention, the switch comprises first mobile stop means rigidly fixed to the optical means, so that they can pivot with the optical means, and second fixed stop means arranged in a plane approximately parallel to the main face of the substrate and cooperating with the first stop means to fix the said active position of the optical means.
The driving means may be electrostatic means or electromagnetic means.
The pivot axis of the optical means and of the first stop means is preferably parallel to the main face of the substrate.
Since the fixed stop means are parallel to the main face of the substrate, it is possible to adjust the position of the fixed stop means very easily and very precisely. Since the mobile stop means are rigidly fixed to the optical means, the active position of the optical means is also precisely fixed by adjustment of the fixed stop means.
Since the fixed stop means according to the invention may be parallel to the main plane, the precision at which these means are formed is related to the precision of the layer thicknesses. On the other hand, in prior art, these stop means were made by the wall of the recess in the substrate which was perpendicular to the plane of the substrate, and the precision of the position of the optical means was then dependent on the precision of the assembly. This is not the case in the invention.
According to a particular embodiment of the switch, there may be an angular spacing between the mobile stop means and the optical means. Due to the rigid link between the mobile stop means and the optical means, this angle is not changed during the pivoting movement of the optical means.
Thus in the invention, the optical function and the positioning function are dissociated, which is not the case in prior art in which the optical means and the mobile stop were in a parallel plane.
Due to the angular spacing, the stop means are not located in the same plane as the optical means. More precisely, the stop means are outside a plane parallel to a plane containing the optical means in the active position. Therefore, there is no risk of interaction with light and there is no need for a particular antireflection treatment to prevent parasite reflection.
For example, the angle formed by the mobile stop means and the optical means may be a right angle. In this case, if the main face of the substrate comprises fixed stop means, the optical means may be switched such that the optical means extend approximately parallel to the main face of the substrate when in the rest position, and the optical means are approximately perpendicular to the main face of the substrate in at least one of the active positions.
According to another particular aspect of the invention, the driving means may comprise at least one first electrode called the mobile electrode fixed to the optical means so that they can pivot with the optical means, and at least one second electrode called the fixed electrode, fixed to the substrate. A fixed electrode is associated with each mobile electrode, to apply electrostatic pivoting forces between the mobile electrode and the associated fixed electrode.
Advantageously, the first stop means, in other words the mobile stop means fixed to the optical means, may form one or several mobile electrode(s) or may carry one or several mobile electrode(s). The stop means then also perform the function of activating the optical means.
In the special case in which there is an angular spacing between the stop means and the optical means, it is possible to separate the electrode plane from the optical means plane, and thus release optical means from constraints related to the presence of an electrode. This enables a wider choice of the optical means.
In particular, the optical means may comprise one or several optical components, for example chosen from among a mirror, a separating strip, a lens, a strip of absorbent material and a strip of reflecting material, and a diffractive lens.
When the driving means are of the electromagnetic type, the electrodes are replaced by magnetic coils.
In a more sophisticated embodiment of a switch with several active positions, the optical means may have a first part with a first optical property upright on the substrate in a first active position, and a second part with a second optical property different from the first optical property or the same as the first optical property, upright on the substrate in a second active position.
These optical means and the mobile stop means may be pivoted by hinge means connecting them to the substrate.
The hinge means may for example comprise one or several torsion beams extending approximately along the pivot axis.
The torsion beams may also automatically return the optical means into either the active position or the rest position.
The invention also relates to an optical cross connecting device comprising several optical switches like those described above arranged in lines and rows, an optical input channel being associated with each line or row, switches and an optical output channel being associated with each row or line of switches.
The optical cross connecting device may also comprise several optical fibres coupled to the corresponding lines and rows of optical switches. Each fibre is thus associated with an input channel or an output channel of the device.
The invention also relates to a process for making a switch like that described. The process comprises the following steps in sequence:
a) the formation of at least one fixed electrode on a main face of a first substrate, and definition of optical means on a second substrate, parallel to a main face of the second substrate,
b) assembly of the fist and second substrates, by putting the said main faces facing each other and
c) etching of the second substrate by a free rear face opposite the main face, to form at least one mobile stop in the substrate, rigidly fixed to the optical means, and to release the optical means.
The mobile stop formed in the second substrate may act as a support for the mobile electrode or may form a mobile electrode itself when the substrate material is not insulating. A non-insulating material is a conducting material or a semiconducting material to which an electrical potential may be applied that can generate the electrostatic force necessary to pivot the optical means.
Note also that several stops and/or several mobile electrodes may be formed simultaneously or not simultaneously.
Step a) in the process may also comprise etching of at least one cavity for reception of the optical means in the first substrate.
The cavity holds optical means, particularly in their rest position, such that they completely release a space for passage of the light beam to be switched.
Furthermore, step a) in the process may include the definition of one or several fixed stops in the first substrate, cooperating with the mobile stop in the second substrate, to fix a position of the optical means in the active position and/or the rest position.
The fixed stops form fixed stop means and give a better definition of the active or rest position of optical means. If there are no stops, the fixed stop means may simply be formed by the surface of the main face of the first substrate.
Other characteristics and advantages of the invention will become clearer from the description made with reference to the figures in the attached drawings. This description is provided purely for illustrative purposes and is in no way limitative.